\begin{tikzpicture}
    \draw (2, 0) circle [x radius=2, y radius=1];
    \node at (2, -1.5) {单项式集合};

    \node at (0.8, 0.5) {$abc$};
    \node at (2.8, -0.5) {……};
\end{tikzpicture}
